I really like the sound of my uke played with a plectrum, but I'm not used to nylon stringed instruments -- will using a light guitar plectrum ruin the strings, does anyone know?
I don't think a plectrum would necessarily "ruin" the strings, although it might cause them to wear out a little sooner. I think the bigger problem would be scratches on the uke's finish from aggressive strumming. Acoustic guitars typically have a pick guard to protect the finish.
When you think about it, a plectrum would be no harder on a Uke (or guitar) than long finger nails.
Also, have seen pro players on YouTube us thumb picks. Have also seen a lot of well used Ukes with finger nail scratches.
Just go for the sound you like best and what works for you.
I've had good luck with rubber "Wedgie" picks. Get the softest they make, which is the thin white one. They're hard to find. I only found thick mediums at the local store. I ordered a variety pack online and tried them all before I settled on the thin ones.
I make felt picks by sandwiching a .60 Dunlop nylon pick between two pieces of sticky-back felt from WalMart... Works a charm. Not stiff like the felt 'uke' picks...